Mold mixture



Patented June 5, 1923.

UNITED STATES 1,457,375 PATENT OFFICE.

VICTOR LOUGHEED, OF SAN FRANCISCO, CALIFORNIA, ASSIGNOR, TO ENTERPRISEFOUNDRY COMPANY, OF SAN FRANCISCO, CALIFORNIA, A CORPORATION OF CALI-FOBNIA.

No Drawing.

To all whom it may concern Be it known that I, VIo'roR Louermno, acitizen of thellnited States, and a resident of San Francisco, in thecounty of San Francisco and State of California, have invented certainnew and useful Improvements in Mold Mixtures, of which the following isa specification. 4

In making certain kinds of highly accurate castings, such as dentalinlays and small brass or other-machine parts, the result is secured byproviding a pattern of wax or other similar material cast or molded in ametal or other die, with or without subsequent finishing, and coatingand surrounding this pattern with mold or investing material from which,after the mold is hardened or set, the pattern is removed by theexpedient of melting, dissolving, or burning out the wax, after whichthe casting is produced by pouring molten metal into the cavity. It isknown that when a very refractory metal is used in this system' ofcasting, the mold material, if a good heat conductor, will chill themetal too rapidly and prevent it from filling the mold completely. Inaddition to this the desirability has been recognized of having thefinished mold of a porous nature so as to vent, more or less freely fromits interior, air and gases which, if retained, will form blow-holes andrender the finished casting unsound. When a metal is used for the castinwhich is highl reactive as to a material 0 the mold it wil tend toattack the mold. The reaction will be particularly favored if the volumeof. the casting is great so that it remains fluid for a relatively longperiod of time, and even though it be small, if the 40 heat conductivityof the mold material is so low that in spite of small casting volume thecasting remains fluid for a relatively long period of time. Because ofthese conditions, it is desirable that the mold material be constitutedof refractory oxldes or other compounds which are not readily reduced ata high temperature in the pres-' ence of the molten metal used for thecastings. The exclusive use of such constituents, so'however, introducesdifliculties in the way of manufacturing and handling the molds,particularly with respect to the proper bindmg to ther of the moldconstituents; and these dilficulties are hard to overcome by the 66 moreselection of substances that act as a mo'ni: MIXTURE.

Application filed August 18, 1919. Serial No. 318,209.

. metal.

In the particular case of the use of calcium sulphate as a binder formolds in which copper-containing alloys are to be cast, it is usual toheat the mold in preparation for pouring the metal, in order to. firstdrive off the water of hydration from the calcium sulphate. But unlessthe temperature reached be excessively high and prolonged, the sulphurtrioxide molecule will remain in combination with. the calcium oxidemolecule, and subsequently be reduced in contact with the hot metal,with the result that the copper of the poured metal will combine with.the sulphur and produce, over the surface of the casting, a coating ofindigo-blue copper sulphide varying in thickness according to the massof the individual casting and the time during which it remains molten incontact with the mold materiaL- This coating is exceedingly diflicult toremove and seriously impairs the accuracy and finish of the castings;

.The object of my invention is to provide a mold composition or mold inwhich, for

convenience of production, calcium sulphate is used as one ofthe'ingredients, but-from which this compound is subsequently removed orchemically broken up, and, if necessary, replaced by another bindermaterial. To this end, in addition to the calcium su1- phate,kieselguhr, and other ingredients of which the mold may be made, Iintroduce a prcglprtion of carbon, preferably in the form ofely-powdered'wood charcoal, or of metallic aluminum in the formof finepowder, or other in edient or ingredients, which, when heate willcombine with either the oxygen or the sulfur of the sulfur trioxidemolecule to the end of substituting in the mold a compound of sulfurirreducible under the conditions subsequently to be encountered, or elsevolatile so that it will be dissipated from the mold in gaseous form. I.find it desirable,'although not absolutely essential, to also introducea small percentage of kaolin, or china clay, (hydrous alumi numsilicate) which will combine with the other materials ofthe mold at ahigh temperature, and then act as a binder. It is desirable that thereducing material be present in exactly molecular proportions, or inexcess of'these, to insure the complete reduction of all of the S thatis present.

I claim: I

1. Ag-porous mold for casting metal, said mold being composed mainly ofa refractory porous substance and containing calcium sulphate limited inquantity to that suflicient for binding together the said substancewithout destroying its porosity, and a basic substance capable ofcombining with the trioxide element of the binder and limited inquantity to that sufiicient to render said element non-reactive withrespect to the metal to be cast. 2

2. A porous mold forvcalsting metal composed mainly of a body ofrefractory porous material together with calcium sulphate limited inquantity to that sufiicient to bind ing the capacity to combine with thesulphuric oxide of the binder and render it nonreactive as to the metalto be cast; said basic substance being in finely divided form butinsufiicient in quantity to impair the porosity of the mold.

Signed at Chicago, Illinois,- this th day of July, 1919.

; VICTOR LOUGHEED.

